I recently replaced the master brake cylinder on my S70. The peddle was firm but there seemed to be a lag between the time the brake pedal was pressed and the brakes engaging. The new master cyliner fixed the problem and brakes work fine again. I got the master brake cylinder from NAPA for about $210. The Haynes Service manual details the repair process.

I did not replace a master cyl on a volvo but on other cars where I did the following symptoms occurred:

1) soft brake pedal. Bearing down on the pedal with your weight will cause it to sink. Even with a good master cyl it may go down quite a bit. With a bad one it will sink all the way to its stop (perhaps after a minute or two) and you will feel when this happens. It may be a leak between the compartments of the cylinder without necessarily any loss of fluid to the outside.


2) particles in the brake fluid, visible either in the master cyl reservoir or after bleeding a bit of fluid out through one or more calipers. These would be bits from a damaged seal.

If the car pulled on braking without other symptoms I would first check if one wheel gets much hotter than the others (indicating that wheel's caliper is sticking) - also the pads on that wheel would probably wear prematurely.

Then I would look for any suspension or alignment issue such as a loose ball joint. This could affect the tracking of the car in different ways depending on acceleration, coasting, turning or braking, as the load on the offending part shifts.